[ruby.parslet] Trouble with dynamic nested parsing

[Dave Townsend]

Hi all,

I'm having trouble getting Parslet 1.6.2 to parse nested tags dynamically.
Here's a baby version of my code:

-------
require 'parslet'

class SimpleNestParser < Parslet::Parser
  rule(:id) { match('[a-z]') }

  rule(:tag) {
    str('<') >> id.capture(:tagname) >> str('>') >>
    tag.maybe >>
    str('</') >> dynamic { |src,ctx| str(ctx.captures[:tagname]) } >>
str('>')
  }

  root(:tag)
end

SimpleNestParser.new.parse "<a><b></b></a>"
-------

I would expect the parse to succeed, but it fails:

-------
/Library/Ruby/Gems/2.0.0/gems/parslet-1.6.2/lib/parslet/cause.rb:63:in
`raise': Failed to match sequence ('<' (:tagname = ID) '>' TAG? '</'
dynamic { ... } '>') at line 1 char 13. (Parslet::ParseFailed)
-------

If I change the dynamic matcher to "match('[ab]')" then the parse does
succeed, which makes it seem that I'm not trying to do anything that
Parslet can't handle.  (But it's important that I match blocks exactly, so
I can't use this as a permanent solution.)

By adding "$stderr.puts ctx.captures[:tagname]" within the dynamic block, I
can see that the block is executed four times, and the value is always "b",
which seems suspicious. I would have thought to have seen at least one "a"
in there.

Am I misunderstanding how to use Parslet in general or the dynamic block in
particular?

Thanks for any guidance the list can provide on how to get my grammar
working!
Dave Townsend